SATA2 is a new standard that is coming out on some high end motherboards. The drives are not readily available yet. They claim this will have 300 Mb /sec transfer, whereas the current SATA drives have about 150 Mb/sec.

I run 2 WD raptors (raid 1 mirror) on my tower PC. That thing runs extremly fast with that setup.

Due to the limitations of the rest of the hardware in a system, it may be a while before you can see the full benifit of SATA2.